1. Technical Field
The present invention relates to a work machine such as a motor-driven lawn mower or a sweeper used in fields or grounds such as golf fields and soccer grounds, banks of a river, parks and green, and gardens, and components thereof.
2. Background Art
Golf fields with two or more courses mow the lawn several times a year. Mowing putting green or fairway of a golf field is done by driving a lawn mower with an operator or by the remote control of it on which wired or wireless remote control device is mounted.
Golf fields have a large lawned area. In particular, putting green requires having proper lawn surface with equal height of the cut with high accuracy while avoiding any patches of grass left unmowed. With this regard, the operator typically observes the actual movement of the lawn mower with his or her eyes and controls a controller to determine an area or path to be mowed, when the lawn mower is controlled remotely. This means that the operator is bound to stay somewhere near the work area. In addition, when it is necessary to make several passes on the same point, no operation can be done exactly in a same way if the operation relies on the memory and feeling of the operator. These operations cannot be done during the night time because the lawn motor is not visible from the operator.
Automatic lawn mowing can save costs such as labor costs and improve the usability of the golf field when the lawn mowing is done during the night time.
For this kind of laborsaving, remote control devices are used. For example, an autonomous lawn mower disclosed in Japanese Patent Laid-Open No. 9-37610 comprises an autonomous navigation device and an electric navigation device. If the electric navigation device is not available, autonomous navigation is used for automatic operation. On the other hand, if the electric navigation device is available, the current point of location obtained by the autonomous navigation is corrected. Errors in angles detected by a sensor for sensing the orientation of the lawn mower are accumulated, so that the lawn mower is alternately rotated by an equal amount in both the right and left directions in order to avoid rotation of the lawn mower in one direction. This achieves more accurate automatic operation of the lawn mower.
A self-propelled machine (lawn mower) disclosed in Japanese Patent Laid-Open No. 2001-344017 uses a personal computer in an off-line mode to generate map data based on survey data obtained when the self-propelled machine travels in a work area. This map data is used to generate operation data and a traveling path in the work area within which the self-propelled machine is going to operate. If the work area has an uneven ground surface, a change in overlapped width due to the slope of the uneven ground surface is calculated and a gap between paths is generated with which the determined overlapped width can be achieved. As a result, even on the uneven ground surface, the paths are defined with different gaps between them depending on the angle of tilt, which contributes to avoiding any patches of grass left unmowed.
The lawn mower disclosed in Japanese Patent Laid-Open No. 9-37610 describes that errors in angles detected by the sensor for sensing the orientation of driving are not accumulated. This means that the accuracy of the angle detection can be improved. However, this lawn mower moves horizontally by an amount equal to a mowing width by means of steering the lawn mower in such a manner that the right steering angle becomes equal to the left steering angle only during the time when the lawn mower moves ahead. Backward movement of the lawn mower is not taken into consideration. In addition, a process of steering and a target area are limited due to the necessary steps of preventing accumulation of the angle detection errors, which restricts the flexibility of the operation. In addition, the lawn is mown always in a semi-circular shape at the start and end points of lawn mowing, with a possibility of leaving patches of grass unmowed.
On the contrary, the lawn mower disclosed in Japanese Patent Laid-Open No. 2001-344017 can avoid any patches of grass left unmowed. However, this lawn mower turns along a semi-circular path at the end of a straight service path. This means that it is impossible to mow the lawn along a path that is smaller than the minimum turning radius of the lawn mower regardless of the width of the cutting blade(s).
The aforementioned problems associated with the lawn mowers disclosed in Japanese Patent Laid-Open Nos. 9-37610 and 2001-344017 also occur in driving cultivating machines such as tractor for agricultural or farm works as well as driving of sweeper or cleaner robots.
An object of the present invention is to provide a work machine and components thereof with which a work path that the work machine follows, including backward movement and turns, can be defined, the work machine being moved through a minimum path in a flexible target area with flexible steering operation.